Art of radiosignaling



L. CQHEN ET AL 1,798,012

ART OF RADIOSIGNALING Filed March 2, 1 927 2 Sheets-Sheet l IN VB'VTORE ,4 011/5 Cami/V 7 March 1931- COHEN ET AL ifi gfli ART OF RADIOSIGNALING Filed March 2, 1927 '2 Sheets-Sheet 2 INI/ENTGKS .4 00/5 60/7 15 1 ,406 0ST flan/D Patented Mar. 24, 1931 UNITED STATES:

PATENT oFElcE LOUIS COHEN, or WASHINGTON, DISTRICT or COLUMBIA, 'AND AUGUST HUNT), or

BATTERY PARK, MARYLAND ART or RAnIosIGNALING Application filed March 2,

This invention relates to an improvement in the art of reception of radio signals.

lfhe object of the invention is to provide an improved method of tuning. Another '5 object is to provide a tuned radio frequency amplifier in which the improved method of. tuning is employed. Still another object is to secure eliminationof regeneration'in the tuned radio frequency amplifier.

.10 In the reception of radio signals, particularly broadcast reception, where considerable volume is'required, tuned radio frequency as well as audio frequency amplifiers are used. Itis the general practice at present to use two or more stages of tuned radio frequency amplification, a detector tube and two stages of audio frequency amplification. The great est difficulty experienced in receivers of this kind is the regeneration due to the inevitable interaction between plate and grid circuits of each unit in the tuned amplifier due to the plate grid capacity within the tube itself, and also 'due to the interaction, magnetic.

and static, of the tuning elements of the sev- .25 eral radio frequency tuning units, which is particularly marked when more than 'two stages of radio frequency amplification is employed. Several methods of neutralization or stabilization have been proposed to overcome this difliculty. all of which have certain advantages as well as disadvantages. It is the purpose of this invention to provide a novel method of tuning which when employed in connection'with a tuned radio frequency amplifier automatically counteracts any tendency towards regeneration, thus securing stability, freedom from electrical impulses caused by regeneration, frequently causing what is commonly designated as.

4.9 whistling, and at the same time simple in design and operation.

i In the drawings Figuresl and 2 show tuning units illustrating the method of tuningemploydin this invention.

V Figure 3 illustrates a typical embodiment of the tuning elements in a complete radio receiver. 7 I

Figure 4.- shows an arrangement for the simultanenous tuning ofseveral circuits all 1927. Serial No. 172,016.

embodying the method of tuning of this invention. I r

Figure 5 is another modification showing a somewhat different method for connecting the tuning circuits ina complete radio receiver, and y Figure 6 is a modification in which the antenna is coupled to the receiver. 7 r In Figure 1, a typical tuning circuit is shown comprising an inductance coil 1, 'a fixed condenser 2, connected in series. Alterhating current energy may be supplied to the circuit by any of the well-known methods, either through direct connection of an energy source 3-as shown in the figure, or through a coupling of some kind. The inductance coil 1 is surrounded by a metal tube 4 with suificient separation between the coil and the metal tube, to permit free movement of the coil within the metal tube, that is the sliding of the coil in and out of the metal" tube, and it is by this movement of the'coil, with respect to the metal tube that tuning is effected. Whenfthe coil is all the way in the metal tube, the variable magnetic field of the coil produced by a variable current flowin the coil induces circular currents inthe closed metallic tube, which in turn set up a magnetic field substantially in opposite direction to that originally produced by the current in the coil,-partly neutralizing the original magnetic field, and thus reducing the effective inductance of the coil. Also, because of the close proximity of the metal tube to the coil, the current in the coil is partly shunted through condenser effects from the coil to'the metal tube to other portions of the coil, and thus assist further in reducing the effective inductance of the coil. As the coil is gradually removed from the metal tube, the inductance of the coil is gradually increased until it regains its normal value when it is completely removed from the metal tube. We have found in practice that itis entirely feasible to design a coil in the matter ofdiameter and windings to secure a considerable range of inductance variation which when combined with a condenser of suitable size will giv'e'a tuning range to cover a desired range of wavelengths. ;W1th,a-co1l of one inch in diameter wound with 125 turns to a length of about three inches, and a metal tube of about three inches and with a condenser of .0005 mf., we had a tuning range from 220 to about 500 meters, covering the present broadcastrange. To cover any other range'of wave lengths is merely'a'm'atte'r of changing the dimensions of the coil and the sizes of the condenser. 7 It is immaterial whether the coil is moved with respect to the metal tube or the metal tube is moved with respect to the coil. Various mechanical devices may be readily devised to effect the movement of the coil with respect to the metal tube or vice versa.

- In Figure 2 a "modification is shown in which the windings. on coil 5 are notuniformly'spaced, the separation between-adjacent turns gradually increasing along the coil from one-end of thecoilto the other end, which is for the purpose of securing a more nearly uniform tuning,that'is, more nearly equal movement ofqcoil with respect to the metal tube or vice versa, for equal changes in frequency over the range of frequencies for. which the circuit is designed. Figure 3 illustrates our invention showing the embodiment of the method of tuning described in connection with Figures 1 and 2, in a complete receiver including 3 stages of tuned radio frequency amplification. The antenna 6 is coupled to the tuning circuit 7'-8 by a small condenser 9, the tuning of the circuit 78 is effected by the movement of the metal tubelO; the terminal 12 of the tuning circuit, a junction point of the inductance coil 7 and condenser 8,'isgrounded at 11. A switch 13 is also provided for connecting thecoupli-ng antenna condenser 9' either to the upper junction point 14 of'the' tuning circuit, or to some other point on the inductance coil 7 at 14', the latter connection giving somewhat'sharper tuning of the antenna circuit system. The terminals 12 and 14 of the antennatuning circuit are connected to the. grid and filament-of the first amplifier tube 16, the connection to the filament being through a biasing grid battery (C) 17; common plate battery 18; filament battery 19 and grid bias battery-17 to all three amplifier tubes 16, 20 and 21 as indicated in the drawings, 55, 56 and '57 are by pass condensers. Theplate 22' of amplifier tube 16 is connected through :a coupling coil 23 to the positive terminal of the plate'battery 18. The tuned grid filament-circuit of thesecond amplifier tube 20, which comprises inductance coils 24 and 25 and condenser 26 is coupled through transformer 27 to the plate circuits 22, 23, 18 of the first amplifier tube 16. The tuning of the circuit is-elfected by the sliding'movement of the metal tube 28 over the inductance coil 25. The movement of the metaltube 28 along the inductance coil 2,5Sis to extend' only up, to

the lower part of the coil 24 which is the secondary of the transformer 27. The induc tance coils 25 may be of the uniform winding type described in connection wth Figure 1, or the non-uniform winding type described in connection with Figure 2. The coupling of amplifier tube 20 to the tuning circuit 29 and the method of tuning circuit 29 is precisely the same as that described in connec tion with the circuit 24; 25, 26 audits coupling to 23. Similarly the tuning of circuit 30, and its coupling to the plate circuit of amplifier tube 21 is also the same as that describedein connection with the tuning circuit 24, 25, 26. The terminals 31 and 32 of the tuning ci-rciut 30 connect to a detectorftube which may be succeeded by an audio amplification in the usual way. i

In'a'll of the radio-frequency circuits the tuning of the circuits are effected by-the movement of the metal tubes over the inductanceucoils. This offers several important acvantages; eliminates the use of variable condensers; simpler to effect simultaneous.

control ofthe tuning; of the several circuits; and most important ofall regenerative effects are practically eliminated. The greatest difiiculty in multistage radio frequency amplification is that due to regeneration caused byleither theinterior of the valve action of each individual unit, or the interaction, magnetic and'st'atic between the circuits of the different amplifying units which tends tion of resistance in each circuit is not constant, but increases asthe metal tube is moved more and more over the coil, whi'chmeans that more and r'nore resistance is introduced into each circuit as the circuit is tuned for higher and higher frequency which is just what is necessary to avoid instability due to regeneration at all frequencies. Also the'in closure of the inductance coils in metal tubes serves as a means of shielding insome degree which assists further in preventing regeneration. ;,This fully supported byexperience; we have built and operated a threestage tuned radio frequency amplifier which gives good amplification andselectivity for the entirebroadcast range without any regenerative elfects which could be in any-way perceived in 1 the practical .ope'ration of. the system. Thissystemis well adapted. foruse to create, a condition of instability. Various in connection with short waves below 200 meters.

Figure 4 illustrates a method for the simultaneous control by one movement the tuning of several independent circuits. In this figure four tuning circuits are shown each consisting of an inductance coil and a fixed condenser indicated by 33-37 34-38; 3539; 36--40. The tuning of each of these circuits is efiected by the movement of the metal tubes indicated by 41, 42, 43 and 44 over each of the inductance coils of the circuit. The four metal tubes 41, 42. 43 and 44 are rigidly connected mechanically through the arms 45 and all can be operated by the handle 46 which controls the simultaneous movement of all of the four metal tubes, and thus controls the simultaneous tuning of all of the four circuits.

The embodiment of the invention illustrated in Figure 5 is, a modification of that shown in Figure 3 which consists in a different method of energy transfer between adjacent radio frequency amplifier tubes. An impedance 47 is provided in the plate circuits of each radio frequency amplifier tube, connected in between the plate and the positive terminal of the plate battery, and the tuned grid circuit of the succeeding tube is connected through condenser 49 to the plate of the preceding amplifier tube. By this arrangement the impedance 47 which may be either a choke coil or simply a resistance provides a ready path for the direct current flow between filament and plate, and shunts the high frequency current resulting from the effect of the received signals into the tuned circuit 48. The condenser 49 serves the purpose of preventing the plate voltage of each tube from biasing the grid of the succeeding tube.

Another modification is shown in Figure 6 in which the antenna 6 is connected through coupling coil 50 to ground 54; the antenna circuit being coupledto the first tuned circuit 51, 53 through a transformer action from 50 on 51.

We claim 1 1. In a multi-tuned circuit system comprising several independent tuning circuits, each of said independent tuning circuits consisting of an inductance coil and condenser,a metal tube surrounding each of said inductance coils, means for connecting all of the said metal tubes whereby the tuning of all of said tuning circuits may be effected simultaneously by a movement of the metal tubes over the said inductances.

' 2. In a multi-tuned circuit system comprising several independent tuning circuits, each of said independent tuning circuits consist ing of an inductance coil and condenser, a metal tube surrounding each of said inductance coils, means for connecting all of the said metal tubes whereby the simultaneous tuning of each of said independent circuits may be effected by a single movement of the said connected metal tubes.

3. In a system for the reception of radio signals comprising an antenna circuit, a tuned multi-stage radio frequency amplifier, a detector and an audio frequency amplifier; the plate circuit of each tube of the said radio frequency amplifier being coupled through a transformer to a tuned circuit which connects to the grid filament of the succeeding tube; each of said tuning circuits comprising an inductance and a fixed condenser, the said inductance of each said tuned circuit being surrounded by a metal tube, and the tuning of each of said circuits being effected by the movement of the said metal tube over the said inductance coil.

4. A system for tunedradio frequency amplification, comprising several stages of am plification, each amplifying unit including an 1ndependent tuning circuit compr sing an inductance C011, wherein the spacing between turns is non-uniform, and a condenser, a me tallic tube surrounding said inductance coil and capable of relative movement thereto, whereby the tuning effect and resistance is proportional to the relative position of the coil and the metal tube surrounding the same.

5. A" system for tuned radio frequency am- .plification, compr1s1ng several stages of application, each amplifying unit including an independent tuning circuit comprising an inductance coil, wherein the spacing between turns is non-uniform, and acondenser, a metallic tube surrounding said inductance coil and capable of relative movement thereto, whereby the tuning effect and resistance is proportional to the relative position of the coil and the metal tube surrounding the same, 5.

where-by a direct linear relation is obtained between the relative movement of the metal tube with respect to the coil and the frequencies for which the system is tuned.

6. In a system for radio frequency amplification, a plurality of amplifying units, each unit 1nclud1ng an independent tuning circuit comprislng an inductance C011 and a condenser, a metallic tube surrounding said inductance coil and means for mechanically connecting all of said tubes whereby said metal tubes can be moved simultaneously by a single control member thereby efiecting simultaneously the tuning of all of the said tuning circuits of the said am lifying system, and also automatically introd iicing the neces sary amounts of resistances in each of said tuning circuits to prevent regeneration in either of these amplifying units.

In testimony whereof we hereunto affix our signatures.

LOUIS COHEN. AUGUST HUND. 

